This invention relates to a high-density type flexible disk drive and, in particular, to a method of controlling a spindle motor for use in the high-density type flexible disk drive.
As is well known in the art, a flexible or floppy disk drive (which may be abbreviated to "FDD") is a device for carrying out data recording and reproducing operation to and from a magnetic disk medium of a flexible or floppy disk (which may be abbreviated to "FD") inserted therein. In recent years, the FDs have been improved to have a greater capacity. Specifically, development has been made of FDs having the storage capacity of 128 Mbytes (which may be called large-capacity FDs) in contrast with FDs having storage capacity of 1 Mbyte or 2 Mbytes (which may be called small-capacity FDs). Following such development, the FDDs have also been improved to accept the large-capacity FDs for data recording and reproducing operations to and from the magnetic disk media of the large-capacity FDs.
Throughout the present specification, FDDs capable of recording/reproducing data for magnetic disk media of the large-capacity FDs alone will be referred to high-density exclusive type FDDs. On the other hand, FDDs capable of recording/reproducing data for magnetic disk media of the small-capacity FDs alone will be called low-density exclusive type FDDs. Furthermore, FDDs capable of recording/reproducing data for magnetic disk media of both the large-capacity and the small-capacity FDs will be called high-density/low-density compatible type FDDs. In addition, the high-density exclusive type FDDs and the high-density/low-density compatible type FDDs will collectively be called high-density type FDDs.
The low-density exclusive type FDD and the high-density type FDD are different in mechanism from each other in several respects, one of which will presently be described. In either FDD, a magnetic head is supported by a carriage which is driven by a drive arrangement to move in a predetermined radial direction with respect to the magnetic disk medium of the FD inserted in the FDD. The difference resides in the structure of the drive arrangement. More specifically, the low-density exclusive type FDD uses a stepping motor as the drive arrangement. On the other hand, the high-density type FDD uses a linear motor such as a voice coil motor (which may be abbreviated to "VCM") as the drive arrangement.
Now, description will be made with respect to the voice coil motor used as the drive arrangement in the high-density type FDD. The voice coil motor comprises a voice coil and a magnetic circuit. The voice coil is disposed on the carriage at a rear side and is wound around a drive axis extending in parallel to the predetermined radial direction. The magnetic circuit generates a magnetic field in a direction intersecting that of an electric current flowing through the voice coil. With this structure, by causing the electric current to flow through the voice coil in a direction intersecting that of the magnetic field generated by the magnetic circuit, a drive force occurs in a direction extending to the drive axis on the basis of interaction of the electric current with the magnetic field. The drive force causes the voice coil motor to move the carriage in the predetermined radial direction.
Another difference between the low-density exclusive type FDD and the high-density type FDD resides in the revolution speed of a spindle motor for rotating the magnetic disk medium of the FD inserted therein. More specifically, the low-density exclusive type FDD can admit the small-capacity FD alone as the FD to be inserted thereinto. As a result, the spindle motor for the low-density exclusive type FDD may rotate the magnetic disk medium of the small-capacity FD inserted therein at a low rotation speed having a revolution speed of either 300 rpm or 360 rpm. On the other hand, the high-density type FDD can admit, as the FD to be inserted thereinto, either the large-capacity FD alone or both of the large-capacity FD and the small-capacity FD. As a result, when the large-capacity FD is inserted in the high-density type FDD, the spindle motor for the high-density type FDD must rotate the magnetic disk medium of the large-capacity FD inserted therein at a high rotation speed of 3600 rpm which is equal to ten or twelve times as large as that of the small-capacity FD.
As a result, it is necessary for the high-density/low-density compatible type FDD to identify and detect whether the FD inserted therein is the large-capacity FD or the small-capacity FD.
In addition, the small-capacity FD and the large-capacity FD are different in structure from each other in several other respects, one of which will presently be described. Both of the large-capacity and the small-capacity FDs have a flat rectangular shape of a width of 90 mm, a length of 94 mm, and a thickness of 3.3 mm in case of a 3.5-inch type. In either FD, a magnetic disk medium of disk-shaped is covered with a case which is called a shell. The case consists of an upper case and a lower case with the magnetic disk medium sandwiched there-between. The lower case of the small-capacity FD is provided with a thin sheet-shaped board having a spring force for applying load to the magnetic disk medium in order to positively carry out chucking of the magnetic disk medium. Such a thin sheet-shaped board is called a lifter. On the other hand, the large-capacity FD is not provided with such a lifter. This is because it is unfavorable for the large-capacity FD to apply the load to the magnetic disk medium because the high-density type FDD must make the magnetic disk medium rotate at the high rotation speed of 3600 rpm as described above.
In the prior art, in a case where the high-density type FDD carries out data recording and reproducing operation to and from the magnetic disk medium of the large-capacity FD inserted therein, the magnetic disk medium of the large-capacity FD is immediately rotated by the spindle motor at the high rotation speed on rotation starting.
In order to rotate the magnetic disk medium of the large-capacity FD by the spindle motor, it is necessary to positively chuck a disk hub of the large-capacity FD on rotation starting of the magnetic disk medium thereof.
More specifically, the disk hub is a disk-shaped metal which is freely received in a circular aperture formed in the lower case of the large-capacity FD at a center portion thereof. The disk hub has a disk center hole at a center portion and a chucking hole (a disk driving oval hole) at a position eccentric with the center portion. The disk hub holds the magnetic disk medium sandwiched between the upper case and the lower case. Accordingly, to rotate the magnetic disk medium may rotate the disk hub by the spindle motor. On the other hand, the spindle motor includes a rotor which comprises a disk holder table, a spindle shaft, and a chucking pin (a drive roller). The disk holder table is for holding the disk hub and is mechanically in contact with the disk hub on rotating of the magnetic disk medium. The spindle shaft is integrally coupled with the disk holder table with the spindle shaft perpendicularly raised from the disk holder table and is freely received in the disk center hole of the disk hub. The chucking pin is upwardly protruded from the disk holder table to move up and down and should be freely received in the chucking hole. That is, to positively chuck the disk hub with respect to the disk holder table, the chucking pin engages with a corner portion of the chucking hole in the disk hub in a radial direction outwardly with the chucking pin freely received in the chucking hole.
While the spindle motor rotates at the high rotation speed immediately on rotation starting in the manner of a conventional starting method for the spindle motor, the disk holder table also rotates at the high rotation speed. In this event, the chucking pin is put into a state buried in the disk holder table without the chucking pin received in the chucking hole. In the very worst case, although the chucking pin is instantaneously received in the chucking hole, there is a possibility of breaking of the chucking pin due to the impact of the chucking pin on the disk hub because the disk holder table rotates at the high rotation speed.